Tag: Max

OM in the News: The Boeing 737 MAX and Reliability

Grounded 737 MAXs

The troubled (and grounded) Boeing 737 MAX, as widely reported, included a new system (MCAS) that automatically deployed when a single sensor detected the danger of a stall. MCAS strongly pushed the nose of the plane down, and pilots could not successfully countermand the activation unless they turned MCAS off. Astoundingly, writes MIT Prof. Arnold Barnett in OR/MS Today (Oct., 2019), “Boeing told airlines nothing about the existence of MCAS, let alone about the procedure to disable it.”  Put bluntly, says Barnett, “MCAS was directly responsible for two fatal crashes, Lion Air Flight 610 in Indonesia and Ethiopian Airlines Flight 302.”

Why did Boeing initially say nothing about MCAS?  The dependence on one sensor violates the principle of redundancy, under which no single failure can cause the loss of the aircraft. Boeing argued that redundancy did exist: the pilots (who were not even told of the existence of MCAS) were the backup system that would disable an improperly deployed MCAS.

There were actually 2 angle-of-attack sensors on the MAX, one of which did not affect MCAS. Boeing devised a cockpit warning light that would come on if the 2 sensors gave highly divergent readings. But a production error meant that the light that was supposedly a standard feature of the MAX could never come on, except when the airline customer bought some optional equipment. Boeing discovered the error in 2017 but did not mention it to airlines until after the first MAX crash a year later.

Now Boeing is fixing the problems with MCAS, with 2 sensors. If one detects a dangerous tilt while the other does not, MCAS will not deploy. But what if the erroneous sensor is the one that says things are normal? More prudent is the policy followed by Airbus, which uses 3 sensors and goes with the majority when there is disagreement. “Given that the feature is standard on Airbus planes,” writes Barnett, “it is far from obvious that having 3 sensors is infeasible or prohibitively expensive.”

Classroom discussion questions:

  1. Which formula in Ch. 17 (Maintenance and Reliability) applies to this issue?
  2.  What impact on airline scheduling is the MAX grounding having?

OM in the News (with video): Boeing’s 4th Generation 737 Takes Shape

If you’ve ever flown, chances are you’ve ridden on a 737. Boeing’s strategy of product enhancement (Ch.5) has made the 737 the best-selling commercial aircraft in history, with 9,745 built since 1968. The newest version, the 737 Max, which is scheduled to make its debut in 2017, is designed with new engines to burn less fuel than its three predecessors, to help airlines’  costs and leave less of a carbon footprint on the environment.

Before the Max, writes USA Today (April 14-15, 2012), there were three versions of the plane: the Original that took flight  in February 1968; the Classics, which began flying passengers in 1984; and the Next Generation, which made its debut in 1998 with new wings and engines that enabled it to go farther and faster  while burning less fuel. All represented enhancements in the original concept of a narrow-body jet with the ability to fly medium to long-haul distances.  (Here is a great time-lapse 2.5 minute video of a 737 being built for Southwest that you can show in class).

At its most basic, the Max will be the same 737 stalwart the public has come to know. It’s a single-aisle jet that will ferry up to 215 passengers, but with higher efficiency. Outfitted with new engines, the Max will use 10% to 12% less fuel than its most current peer, the Next-Generation. That holds particular appeal for airlines, with jet fuel making up 25% to 40% of their costs, and whose profitability is threatened as the price of crude oil stays around $100 a barrel.

Even with Max, demand remains so high for the 737 that Boeing in January began delivering current model 737s at the unprecedented production pace of 35 a month. It plans to ramp up to 42 a month at the start of 2014 . Will a  completely new single-aisle plane will arrive eventually? “It’s something that we’ll definitely do at some point,” says Boeing.

Discussion questions:

1. Why has Boeing chosen product enhancement over a new single aisle plane?

2. How have cell phones been enhanced over the past 2 decades?